Small investors have never had more information or paid lower costs.

This holiday weekend, there's plenty to worry for investors about—sluggish economic growth, unappealing stock valuations, loose monetary policy, volatile markets. But there is at least as much to give thanks for.

"I think there's less for investors to worry about, in a lot of ways, than there used to be," says James Cloonan, who founded the nonprofit American Association of Individual Investors in 1978. "There's more...